Via http://www.pinktentacle.com/2009/07/rice-paddy-art/

At first I thought this was some clever photoshop work, but paddy field art does exist and it is awesome! The process behind the field art is fairly straightforward (grow different colored rice plants on a planned grid), but it's the scale that makes it so impressive. The village of Inakadate in Aomori Prefacture boasts some of the most detailed of the country's crop art, a tradition that dates back to ancient times of...1993.

There's a great article over at The Japan Times Online with a detailed history behind the tradition  http://search.japantimes.co.jp/cgi-bin/fl20070826x1.html/

One last link, to the folks over at weburbanist.com who've compiled a list of crop/aerial art  http://weburbanist.com/2009/02/02/aerial-art-crop-circles/